The following projects are planned: (a) Investigation of rhythmicity in sexual behavior of male rats and possible physiological substrates; (b) determination of the circadian and infradian estradiol rhythms of the female rat in constant light; (c) a study of changes in ovarian morphology due to the exposure of female rats to constant light; (d) determination of the contribution of the adrenal cortex to the constant-light induced disruption of the female estrous cycle; (e) investigation of the effects of self-selection of environmental illumination on the estrous cycle of the golden hamster; (f) measurement of several physiological and behavioral rhythms of the female exposed to continuous light.